To enhance the performance of diesel engines, vehicle manufacturers have begun investigating the use of direct injection fuel systems. In a direct injection fuel system, a fuel injector injects highly pressurized diesel fuel directly into an engine cylinder combustion chamber during the compression stroke. Direct fuel injection can facilitate better mixture of diesel fuel and air, which can lead to a cleaner and more controllable burn, thus enhancing engine performance.
Diesel engines typically rely solely on compression to ignite the fuel/air mixture. Compression pressures within a diesel engine can reach very high levels (e.g., about 2000 Bar or 29,000 psi). Because diesel fuel is injected during the compression stroke, the diesel fuel must also be at a high pressure in order to enter the cylinder. High fuel pressure is typically achieved by using a high-pressure booster pump in conjunction with a low pressure fuel tank pump.
FIG. 1 is a schematic illustration of a conventional direct injection fuel system 5 for a diesel engine. Diesel fuel is pumped from a tank 10 via a low pressure fuel tank pump 12 to a high pressure booster pump 14. The high pressure booster pump 14 raises the pressure of the diesel fuel so that the diesel fuel can enter a combustion chamber against the compression pressure in the cylinder. Typically, a high pressure booster pump is mounted to an engine and is operated directly from a cam (or crank) shaft within the engine. As illustrated in FIG. 1, the high pressure diesel fuel discharged from the high pressure booster pump 14 flows through a fuel rail 16 and to each injector 18 via a respective fuel passageway 20. Each injector 18 is configured to deliver a controlled amount of diesel fuel into a respective cylinder 22 when activated by an engine control unit (ECU) 24. Conventionally, fuel pressure in a fuel rail 16 is controlled via a fuel rail pressure regulator 26 and a fuel rail pressure sensor 28. Typically, the pressure sensor 28 and pressure regulator 26 communicate with each other via an ECU 24.
Because two separate components (i.e., a pressure regulator and a pressure sensor) are typically used to control fuel pressure in conventional direct injection fuel systems, multiple connections in a fuel rail are typically necessary. Unfortunately, each connection in a high pressure fuel rail is a potential source of fuel leakage. Because fuel rails are typically mounted near hot exhaust manifolds, the potential for fire caused by a fuel leak from a high pressure fuel rail can be substantial.